1. Field of the Invention
The present invention relates to an image forming apparatus and is suitably applicable to specifically an image forming apparatus having a fan for cooling a sheet.
2. Description of the Related Art
In recent years, print of a color image forming apparatus has been demanded to be high-speed and consequently, printed sheets are stacked on a discharge stacking unit before heat at the time of ink fixing is cooled. Thus, countermeasures for defects such as sheet adhesion, image rubbing, separation and the like, which occur due to contact between toners particularly at the time of two-side print have been urgently demanded.
When the curl amount of a sheet which is produced by reversing at the time of two-side print is large, it may affect conveyance and transfer of a sheet, print accuracy and the like. More specifically, there are such problems as breaking of a front end, winding of a sheet around a roller, jamming, transfer failure, skewing and thus; therefore, solutions for these problems have been demanded from viewpoints of improvement of print quality.
The sheets stacked on the stacking tray are under high temperatures due to heat at the time of fixing. If the sheet at this high temperature is stacked as it is, toner on an image face is likely to adhere to the sheet. As a consequence, a problem in image defect such as distortion of image face and contamination of sheet rear face may occur. Particularly, when images are formed on two sides, the sheets are stacked successively, so that this problem is likely to occur due to contacts of one toner with another toner.
For the reason, conventionally as a countermeasure thereto, providing a conveying path with a fan so as to lower the sheet temperature has been proposed in Japanese Patent Application Laid-Open No. 2005-148674. In this structure one fan is installed in the duct with the two vents for two sheet trays. Because the distance of the sheets on the trays and the fan is long, there is a possibility that the sheet may not be cooled sufficiently by the fan.
According to Japanese Patent Application Laid-Open No. 2006-011148, a fan is provided on the bottom of the side face of the apparatus below the downstream end of the conveying path. Because the fan cools the sheets in one portion, the fan is not efficiently used. In addition, a sheet to be reversed for forming images on two sides is under a high temperature and when, such a high temperature sheet is conveyed in order to form, an image on the rear face, the temperature within the apparatus compartment is raised or the transfer unit is heated.
Japanese Patent Application Laid-Open No. 2005-196079 has disclosed an image forming apparatus comprising an image reading unit, a fixing apparatus, a reversal paper discharge unit and a motor fan. According to the structure described in the Japanese Patent Application Laid-Open No. 2005-196079, an opening portion of the motor fan is disposed perpendicularly to the conveying direction of the sheet such that it opposes an area containing the image reading unit and the reversal paper discharge unit and a wind passage direction is along the width direction of the sheet. Because the motor fan is disposed on the back side in a direction perpendicular to the conveying direction with respect to the reversal paper discharge unit and a sheet stacking portion, the distance of the motor fan and the cooling object (the reversal paper discharge unit and the sheet stacking portion) is long. Therefore there is a possibility that the sheet may not be cooled sufficiently by the motor fan.
Japanese Patent Application Laid-open No. 2003-307996 has described a structure in which a fan is provided on the side portion of the apparatus in order to discharge air around a discharge stacking means, on which the sheets are to be stacked to the outside. Because there is a conveying path between the fan and the discharge stacking means, a distance between the fan and the sheets stacked on the discharge stacking means is so long that the stacked sheets may not be cooled sufficiently.